U.S. patent application number 13/231010 was filed with the patent office on 2012-03-15 for process for detecting energy theft.
This patent application is currently assigned to Trilliant Networks, Inc.. Invention is credited to Michel Veillette.
Application Number | 20120062210 13/231010 |
Document ID | / |
Family ID | 45806040 |
Filed Date | 2012-03-15 |
United States Patent
Application |
20120062210 |
Kind Code |
A1 |
Veillette; Michel |
March 15, 2012 |
Process for Detecting Energy Theft
Abstract
The present invention relates generally to detecting energy
theft within an energy distribution system and more particularly to
systems and methods for detecting energy discrepancies in voltages
and/or currents reported by electric meters present in a
distribution circuit, without requiring installation of additional
hardware at the transformer. Typically, the location of each of at
least two meters is determined with respect to a transformer. The
line resistances within the distribution circuit are determined
starting with a line resistance farthest from the transformer.
Estimated line voltages are determined for at least one electric
meter using the estimated line resistances, and the estimated
voltages are compared to actual voltage readings for the at least
one electric meter. The existence of line loss is determined based
on this comparison.
Inventors: |
Veillette; Michel;
(Waterloo, CA) |
Assignee: |
Trilliant Networks, Inc.
Redwood City
CA
|
Family ID: |
45806040 |
Appl. No.: |
13/231010 |
Filed: |
September 13, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61382057 |
Sep 13, 2010 |
|
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Current U.S.
Class: |
324/110 |
Current CPC
Class: |
G01D 4/002 20130101;
H04Q 2209/60 20130101; G01R 22/066 20130101; H04Q 9/00 20130101;
Y02B 90/20 20130101; Y04S 20/30 20130101 |
Class at
Publication: |
324/110 |
International
Class: |
G01R 21/00 20060101
G01R021/00 |
Claims
1. A system comprising: a transformer; a first electric meter in
electrical communication with the transformer via a first
electrical line; a second electric meter in electrical
communication with the transformer via a second electrical line,
the second electric meter located a farther distance from the
transformer than the first electric meter; a server in electrical
communication with the transformer, the first electric meter, and
the second electric meter, wherein the server: determines the
location of the first electric meter and the second electric meter
with respect to the transformer; estimates the resistance along the
second electrical line; calculates an expected voltage for the
second electric meter based on the estimated resistance of the
second electrical line; receives one or more actual voltage
readings for the second electric meter; compares the expected
voltage for the second electric meter with the one or more actual
voltage readings for the second electric meter; and determines the
existence of line loss along the second electrical line if said
comparison results in a difference that is greater than a
predetermined threshold.
2. A system according to claim 1, wherein the server: estimates a
resistance along the first electrical line; calculates an expected
voltage for the first electric meter based on the estimated
resistance of the second electrical line and the estimated
resistance of the first electrical line; receives one or more
actual voltage readings for the first electric meter; compares the
calculated expected voltage for the first electric meter with the
one or more actual voltage readings for the first electric meter;
and determines the existence of line loss along the first
electrical line if said comparison results in a difference that is
greater than the predetermined threshold.
3. A system according to claim 1, wherein the locations of the
first and second meters are determined based one or more voltage
samples received from each of the meters.
4. A system according to claim 3, wherein the meter having the
lowest average voltage sample is determined to be located the
farthest from the transistor.
5. A system according to claim 1, wherein said estimating of the
resistance along the second electrical line is based on one or more
instantaneous measurements of the current and voltage from the
first and second electric meters.
6. A system according to claim 5, wherein said estimating of the
resistance along the second electrical line is based on an average
of the one or more instantaneous measurements.
7. A system according to claim 1, wherein an operator is notified
if line loss is detected.
8. A system according to claim 2, wherein said estimating of the
resistance along the first electrical line is based on one or more
instantaneous measurements of the current and voltage from the
first electric meter.
9. A system according to claim 8, wherein said estimating of the
resistance along the first electrical line is based on an average
of the one or more instantaneous measurements.
10. A process for detecting the existence of line loss in electric
meters present in a distribution circuit, the process comprising:
determining, by a processor, the location of each of at least two
meters with respect to a transformer of the distribution circuit,
each of the meters in electrical communication with an electrical
line; estimating, by the processor, a resistance of the electrical
line at the location of each of the at least two meters, starting
with a line resistance farthest from the transformer; calculating,
by the processor, estimated line voltages for at least one electric
meter using the estimated line resistances; receiving, by the
processor, actual voltage readings for the at least one electric
meter; comparing, by the processor, the estimated line voltage with
the actual voltage readings for the at least one electric meter;
and determining, by the processor, the existence of line loss if
one or more of the comparisons result in a difference that is
greater than a predetermined threshold.
12. A process according to claim 10, wherein the location of each
of the at least two meters is determined based one or more voltage
samples received from each of the meters.
13. A process according to claim 12, wherein the location of each
of the at least two meters is determined based on the average of
the one or more voltage samples.
14. A process according to claim 13, wherein the meter having the
lowest average voltage sample is determined to be located the
farthest from the transistor.
15. A process according to claim 12, wherein the location of each
of the at least two meters is determined based on the median of the
one or more voltage samples.
16. A process according to claim 10, wherein said estimating of the
resistance is based on one or more instantaneous measurements of
the current and voltage from the at least two meters.
17. A process according to claim 16, wherein said estimating of the
resistance is based on an average of the one or more instantaneous
measurements.
18. A process according to claim 10, further comprising averaging
the received actual voltage readings from the at least one electric
meter and comparing the averaged actual voltage readings to the
estimated line voltage.
19. A process according to claim 10, wherein the predetermined
threshold is about 10%.
20. A process according to claim 10, wherein an operator is
notified if line loss is detected.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] The present application claims benefit of similarly titled
U.S. provisional patent application Ser. No. 61/382,057 filed Sep.
13, 2010, which is incorporated herein by reference in its
entirety.
FIELD OF THE INVENTION
[0002] The present invention relates generally to detecting energy
theft within an energy distribution system. More particularly, the
present invention relates to systems and methods for detecting
energy discrepancies in voltages and/or currents reported by
different electric meters present in a distribution circuit,
without requiring installation of additional hardware at the
transformer.
BACKGROUND OF THE INVENTION
[0003] Electricity theft is a problem that all electric utilities
face. In fact, it is estimated that energy theft costs utilities
billions of dollars annually, and these losses generally are passed
along to customers in the form of higher rates. Unfortunately,
electricity theft via fraud (meter tampering) or stealing (illegal
connections) can also create situations that endanger lives and
property.
[0004] An existing system and process for detecting energy theft
includes first installing a meter at a distribution transformer.
Energy theft is then detected if the energy measured at the
transformer is greater than the aggregated energy reported by the
electric meters installed at the different premises connected to
the distribution transformer. This method is effective, but
requires installation and maintenance of an extra meter for each
distribution transformer.
[0005] Accordingly, there is a need in the art for systems and
processes that effectively detect or identify potential energy
theft, without the need for additional hardware implementation
beyond the hardware (e.g., electric meters) installed at customer
premises.
SUMMARY OF THE INVENTION
[0006] The exemplary embodiments herein describe a method that
allows detection of energy theft solely based on the analysis of
the information provided by the electric meters at the different
customer premises connected to a transformer. The invention allows
for such detection without the need for additional hardware
installation.
[0007] In one aspect of the invention, a system is provided
including a transformer, a first electric meter, and a second
electric meter connected to a server. The first electric meter is
connected to the transformer via a first electrical line, and the
second electric meter is connected to the transformer via a second
electrical line. The second electric meter is located a farther
distance from the transformer than the first electric meter. The
server determines the location of the first electric meter and the
second electric meter with respect to the transformer. Once the
location of the meters is determined, the server estimates the
resistance along the electrical line located the farthest from the
transistor (i.e., the second electrical line). The server may then
calculate an expected voltage for the second electric meter based
on the estimated resistance of the second electrical line. The
server receives one or more actual voltage readings for the second
electric meter and compares the expected voltage for the second
electric meter with the one or more actual voltage readings for the
second electric meter. The server can determine the existence of
line loss along the second electrical line if there is a difference
between the expected voltage and the actual voltage readings that
is greater than a predetermined threshold.
[0008] In another aspect of the invention, the server may also
estimate the resistance along the first electrical line. The server
calculates an expected voltage for the first electric meter based
on the estimated resistance of the second electrical line and the
estimated resistance of the first electrical line. Actual voltage
readings for the first electric meter are then received, and may be
compared to the calculated expected voltage for the first electric
meter. The server can determine the existence of line loss along
the first electrical line if there is a difference between the
expected voltage and the actual voltage readings that is greater
than a predetermined threshold.
[0009] In yet another aspect of the invention, a process for
detecting the existence of line loss in electric meters present in
a distribution circuit is provided. The process includes
determining, by a processor, the location of each of at least two
meters with respect to a transformer of the distribution circuit,
each of the meters in electrical communication with an electrical
line. The process also includes estimating, by the processor, a
resistance of the electrical line at the location of each of the at
least two meters, starting with a line resistance farthest from the
transformer. Once the resistances are estimated, the process
continues by calculating estimated line voltages for at least one
electric meter using the estimated line resistances. The process
then includes receiving, by the processor, actual voltage readings
for the at least one electric meter such that a comparison of the
estimated line voltage with the actual voltage readings for the at
least one electric meter may be made. Finally, the process includes
determining, by the processor, the existence of line loss if one or
more of the comparisons result in a difference that is greater than
a predetermined threshold.
[0010] These and other aspects of the invention will be better
understood by reading the following detailed description and
appended claims.
BRIEF DESCRIPTION OF THE FIGURES
[0011] FIG. 1 is a schematic showing an example of a residential
distribution circuit with a representative three meters;
[0012] FIG. 2 is a simplified schematic of FIG. 1;
[0013] FIG. 3 is a first subcircuit of the schematic of FIG. 2;
and
[0014] FIG. 4 is a second subcircuit of the schematic of FIG.
2.
DETAILED DESCRIPTION
[0015] All terms used herein are intended to have their ordinary
meaning in the art unless otherwise provided.
[0016] An exemplary embodiment allows for energy theft detection in
a distribution circuit. Typically, a distribution circuit carries
electricity from a transmission system and delivers it to consumer
locations. The distribution circuits described herein typically
comprise a transformer, which reduces distribution voltage to the
relatively low voltages (e.g., 1 kV) required by lighting and
interior wiring systems. The transformer may be pole-mounted or set
on the ground in a protective enclosure. In any event, the
transformer is in electrical communication with any number of
consumer locations via, for example, an "electrical service" or
"service drop" connection (e.g., and electrical wire). Each
consumer location typically comprises a meter to determine the
amount of electricity consumed at the location.
[0017] In one embodiment, the inventive methods require that at
least two electric meters are present in the distribution circuit.
Moreover, instantaneous current and voltage information should be
available from all the delivery points (e.g., meters) within the
transformer.
Equivalent Circuit
[0018] An exemplary residential distribution circuit in is
illustrated in FIG. 1. As shown, the circuit comprises a number of
electric meters (M1, M2, and M3), such as those that are typically
employed in North America to measure electricity usage at a
location (e.g., a home, apartment, other residence, office or the
like). Each of the meters (M1, M2, and M3) are adapted to report an
instantaneous voltage (V1, V2, V3) and instantaneous current (I1a,
I1b, I2a, I2b, I3a, and I3b) corresponding to instantaneous
electricity usage at the location. Moreover, each of the meters may
experience an aggregate load during such electricity usage, which
may be represented in the circuit diagram, for example, by any
number of resistors on both sides of the circuit (e.g., R3a, R3b,
R6a, R6b, R8a, and R8b).
[0019] The electricity distribution circuit is shown to experience
a resistance along the main electricity distribution line. The
resistance may be modeled or represented by any number of resistors
(e.g., R1a, R1b, R4a and R4b). Additionally, the circuit
experiences a resistance along each line feeding to the multiple
locations, wherein such resistance may be represented by any number
of resistors (e.g., R2a, R2b, R5a, R5b, R7a, and R7b).
[0020] Referring to FIG. 2, the schematic of FIG. 1 is shown in a
simplified state, where it assumed that the resistances of the
conductors for both sides of the circuit are equal (i.e., R1a=R1b,
R2a=R2b, R4a=R4b, R6a=R6b, R7a=R7b). As shown, each of the meters
(M1, M2, and M3) reports an instantaneous voltage (V1, V2, V3) and
instantaneous current (I1=I1a+I1b, I2=I2a+I2b, I3-I3a+I3b)
corresponding to instantaneous electricity usage at a location. The
aggregate load experienced by each of the meters (M1, M2, and M3)
on both sides of the circuit (R3=R3a+R3b, R6=R6a+R6b, R8=R8a+R8b)
is shown simply as one resistor per meter.
[0021] The resistance seen along the main electricity distribution
line is represented by resistors R1 and R4, where R1=R1a=R1b and
R4=R4a=R4b. Finally, the resistance along each line feeding to the
multiple premises, is represented by resistors R2, R5, and R7,
respectively, where R2=R2a=R2b; R5=R5a=R5b; and R7=R7a=R7b.
[0022] The exemplary electricity distribution circuit shown in FIG.
2 (and FIG. 1) is a single-phase, 3-wire circuit attached to ANSI
Form 4S or 4A meters. Other types of distribution circuits and
meter forms are possible in North America and throughout the world,
with the inventive methods described herein being applicable to
most of them. For example, for three phase distribution circuits,
one skilled in the art recognizes that the methods described herein
with respect to the exemplary single-phase circuit would need to be
repeated for each of the three phases. Further, since the current
distribution circuit configuration in Europe need only support 220
V services, not both 110 V and 220 V services, a typical European
distribution circuit is in fact equivalent to FIG. 2.
Data Analysis
[0023] Still referring to FIG. 2, the presence of non-measured
energy in a distribution circuit creates discrepancies in the
voltages and currents reported by the different electric meters
(M1, M2, and M3) present in the distribution circuit. It has been
found that detection of these discrepancies provides a good
indication of energy theft and can be used to trigger further
investigation.
[0024] To enable this analysis, all meters (M1, M2, M3) within a
distribution circuit are configured to report instantaneous voltage
(V1, V2, V3) and current (I1, I2, I3) samples periodically. For
example, the meters may be programmed to report voltage and current
readings at time intervals ranging from seconds to hours or even
days. It will be appreciated that such samples may be manually
determined or automatically determined.
[0025] To obtain snapshots in time of the different currents and
voltages within the distribution circuit, all meters may be adapted
to take their measurements simultaneously. Exemplary meters for use
with the embodiments described herein are smart meters and
retrofitted meters that include the necessary communications
hardware and software including at least one microprocessor, radio,
and memory.
[0026] Once the instantaneous voltage and current samples are
procured, the analysis of the information may be completed in the
following three steps:
[0027] 1. Evaluation of the location of each meter within the
distribution line
[0028] 2. Evaluation of the resistance of the different lines
[0029] 3. Verification of consistency in the reported voltages
[0030] In addition to circuitry and meters having the described
measuring and reporting functionality, the system for performing
the evaluation, verification and other steps of the data collection
and analysis processes described herein includes at least a
back-end processor programmed with software for implementing the
processes. One skilled in the art recognizes that multiple
processors, databases, servers, displays and the like may be used
in various combinations to implement the invention. Additionally,
meter data may be communicated to the back-end processor through
wired, wireless or a combination of wired/wireless components and
steps.
[0031] The methods described herein may be implemented within AMI,
AMR, or Advanced Metering Management (AMM) technologies, including
systems that measure, collect and analyze utility usage, from
advanced devices such as electricity meters, through a network on
request or a pre-defined schedule. Such infrastructure typically
includes hardware, software, communications, customer-associated
systems and meter data management software. The infrastructure
collects and distributes information to customers, suppliers,
utility companies and service providers.
[0032] The technology described herein may be incorporated into
systems comprising mesh network technology. Mesh networks typically
include at least one mesh gate and at least one mesh device, such
as an electrical meter. The mesh gate may communicate with the
meters over a mesh network. The mesh gate may also communicate with
a server or processor over a wide area network. The mesh gate may
form a mesh network with nearby meters and interface between the
meters and the server.
Meter Location
[0033] To analyze the data, it is important for the system to know
or determine the position of each meter (M1, M2, M3) relative to
the transformer. In one embodiment, the meter position can be
inferred by analyzing the voltages (V1, V2, V3) reported by each
meter. The meter consistently reporting the highest voltage will
typically be the closest to the transformer. The position of the
other meters may then be determined based on their relative
voltage.
[0034] However, depending on the resistance of the different lines
and the current present on each line, it is possible that the
voltage reported by a meter closer to the transformer may be less
than the voltage reported by meters further down the distribution
line. For this reason, in certain embodiments, the position of each
meter may be determined statistically based on multiple samples.
For example, any number of instantaneous voltage samples may be
determined by the system for each meter. The average of the samples
may be determined for each meter, and meter positions may be
determined based on the average. In other embodiments, the position
of each meter may be determined based on the respective median
sample voltage of each meter. Of course, the location of the meters
may simply be manually entered into the system by, for example, and
operator. The operator may also update the meter position as new
meters are installed or as older meters are removed.
Resistance Estimation
[0035] Still referring to FIG. 2, the resistances (R1, R2, R4, R5,
R7) of the different lines can be estimated by using at least two
samples of the instantaneous voltages and currents. In one
embodiment, this process begins by estimating the resistance of the
line farthest from the transformer (e.g., R7).
[0036] Referring to FIG. 3, a first subcircuit of FIG. 2 is shown.
The voltage (V6) across R5 can be expressed based on the current
and voltage reported by meter M2 (I2, V2) and meter M3 (I3, V3).
The following equations show this relationship for a first sample
(Sample x):
V6x=(R7*I3x)+V3x (1)
V6x=(R5*I2.times.)+V2x (2)
[0037] Using these equations, the relationship between resistances
R5 and R7 may be expressed as follows:
R 5 = ( R 7 * I 3 x ) + V 3 x - V 2 x I 2 x ( 3 ) ##EQU00001##
[0038] A second sample (Sample y) may then be obtained to determine
a second equation for R5:
R 5 = ( R 7 * I 3 y ) + V 3 y - V 2 y I 2 y ( 4 ) ##EQU00002##
[0039] Combining equations 3 and 4, the value of R7 may be
expressed as:
R 7 = ( V 3 y * I 2 x ) + ( V 2 x * I 2 y ) - ( V 2 y * I 2 x ) - (
V 3 x * I 2 y ) ( I 3 x * I 2 y ) - ( I 3 y * I 2 x ) ( 5 )
##EQU00003##
[0040] Using the same technique, the resistance R5 can computed as
follows:
R 5 = ( V 2 y * I 3 x ) + ( V 3 x * I 3 y ) - ( V 3 y * I 3 x ) - (
V 2 x * I 3 y ) ( I 2 x * I 3 y ) - ( I 2 y * I 3 x ) ( 6 )
##EQU00004##
[0041] Each following stage in the distribution circuit can be
estimated using the same method described above. To obtain the same
condition as above, the voltage and current of the distribution
line are estimated using the resistances previously computed. For
example, the corresponding samples of V6 and I6 may be computed
using R7 as follows:
V6x=(R7*I3x)+V3x (7)
V6y=(R7*I3y)+V3y (8)
I6x=I2x+I3x (9)
I6y=I2y+I3y (10)
[0042] Referring to FIG. 4, a second subcircuit of FIG. 2 is shown.
Once the above calculations are computed, the following two
resistances (R2 and R4) can be computed as shown in the equations
below:
R 4 = ( V 6 y * I 1 x ) + ( V 1 x * I 1 y ) - ( V 1 y * I 1 x ) - (
V 6 x * I 1 y ) ( I 6 x * I 1 y ) - ( I 6 y * I 1 x ) ( 11 ) R 2 =
( V 1 y * I 6 x ) + ( V 6 x * I 6 y ) - ( V 6 y * I 6 x ) - ( V 1 x
* I 6 y ) ( I 1 x * I 6 y ) - ( I 1 y * I 6 x ) ( 12 )
##EQU00005##
[0043] The quality of this estimate depends on the precision of the
measurements and the different currents present during these
measurements--a higher current typically produces a more accurate
estimate since measurement errors are smaller relative to the
higher reading. For this reason, multiple sample sets may be used
to produce multiple estimates which may then be averaged or from
which the median value may be ascertained.
[0044] Typically, the samples used should be different to avoid a
division by zero when computing the resistances. Accordingly,
sample sets that produce a division by zero may be discarded.
Voltage Consistency
[0045] Once the location of each meter within the distribution
circuit is known and the different resistances are estimated, each
sample reported by the meters can be used to compare the voltage
reported by the meters and the voltage computed based on the
reference circuit.
[0046] For example, using the reference circuit defined by FIG. 2,
the voltages may be represented as follows:
V5=V1+(R2*I1) (13)
V6=V5-(R4*(I2+I3)) (14)
V2'=V6-(R5*I2) (15)
V3'=V6-(R7*I3) (16)
[0047] The percentage of discrepancy can be computed by comparing
the voltage reported by the meter (V2, V3) and the voltage computed
by the reference circuit (V2', V3'):
% discrepency = absolute ( V 2 ' - V 2 ) V 2 * 100 ( 17 ) %
discrepency = absolute ( V 3 ' - V 3 ) V 3 * 100 ( 18 )
##EQU00006##
[0048] Equations (17) and (18) are reflective of measured
discrepancy with respect to M2 and M3, respectively.
[0049] Possible energy theft is signaled when the percentage of
discrepancy is higher than a certain threshold. For example, if the
percentage of discrepancy of the voltage reported by the meter and
the voltage computed by the reference circuit exceeds about 50%,
about 25%, about 10%, about 5%, about 1% or even about 0.5%, a
possible energy theft may be occurring at the corresponding
location in the distribution circuit. Accordingly, in one
embodiment, if the percent discrepancy exceeds the threshold, the
system may raise a flag or otherwise alert an operator. The
operator may then investigate the discrepancy and correct the
situation
[0050] For simplicity, the different equations presented have been
based on the reference circuit shown in FIG. 2 containing three
electric meters. One skilled in the art recognized that the same
logic applies to any distribution circuit with at least two
meters.
[0051] Unless specifically stated otherwise as apparent from the
foregoing discussion, it is appreciated that throughout the
description, discussions utilizing terms such as "processing" or
"computing" or "calculating" or "determining" or "displaying" or
the like, can refer to the action and processes of a data
processing system, or similar electronic device, that manipulates
and transforms data represented as physical (electronic) quantities
within the system's registers and memories into other data
similarly represented as physical quantities within the system's
memories or registers or other such information storage,
transmission or display devices.
[0052] The exemplary embodiments can relate to an apparatus for
performing one or more of the functions described herein. This
apparatus may be specially constructed for the required purposes,
or it may comprise a general purpose computer selectively activated
or reconfigured by a computer program stored in the computer. Such
a computer program may be stored in a machine (e.g. computer)
readable storage medium, such as, but is not limited to, any type
of disk including floppy disks, optical disks, CD-ROMs and
magnetic-optical disks, read only memories (ROMs), random access
memories (RAMs) erasable programmable ROMs (EPROMs), electrically
erasable programmable ROMs (EEPROMs), magnetic or optical cards, or
any type of media suitable for storing electronic instructions, and
each coupled to a bus.
[0053] Some exemplary embodiments described herein are described as
software executed on at least one processor, though it is
understood that embodiments can be configured in other ways and
retain functionality. The embodiments can be implemented on known
devices such as a server, a personal computer, a special purpose
computer, a programmed microprocessor or microcontroller and
peripheral integrated circuit element(s), and ASIC or other
integrated circuit, a digital signal processor, a hard-wired
electronic or logic circuit such as a discrete element circuit, or
the like. In general, any device capable of implementing the
processes described herein can be used to implement the systems and
techniques according to this invention.
[0054] It is to be appreciated that the various components of the
technology can be located at distant portions of a distributed
network and/or the internet, or within a dedicated secure,
unsecured and/or encrypted system. Thus, it should be appreciated
that the components of the system can be combined into one or more
devices or co-located on a particular node of a distributed
network, such as a telecommunications network. As will be
appreciated from the description, and for reasons of computational
efficiency, the components of the system can be arranged at any
location within a distributed network without affecting the
operation of the system. Moreover, the components could be embedded
in a dedicated machine.
[0055] Furthermore, it should be appreciated that the various links
connecting the elements can be wired or wireless links, or any
combination thereof, or any other known or later developed
element(s) that is capable of supplying and/or communicating data
to and from the connected elements. The terms determine, calculate
and compute, and variations thereof, as used herein are used
interchangeably and include any type of methodology, process,
mathematical operation or technique.
[0056] The invention described and claimed herein is not to be
limited in scope by the specific embodiments herein disclosed since
these embodiments are intended as illustrations of several aspects
of the invention. Any equivalent embodiments are intended to be
within the scope of this invention. Indeed, various modifications
of the invention in addition to those shown and described herein
will become apparent to those skilled in the art from the foregoing
description. Such modifications are also intended to fall within
the scope of the appended claims. All publications cited herein are
incorporated by reference in their entirety.
* * * * *